Generally, dental adhesion is divided into enamel adhesion and dentine adhesion. In case of enamel adhesion, it was found in 1995 by Buonocore that sustainability could be enhanced through changing a soft surface of enamel to a rough surface via acid corrosion in order to facilitate capillary phenomenon development therein. This allows a dental restoration material to permeate through minute pores. As such, excellent physical properties could be achieved via enamel adhesion (see U.S. Pat. Nos. 4,102,856 and 4,131,729, etc).
Furthermore, in case of dentine adhesion, enamel is considered non-live tissue while dentine is considered as being an extension of the dental pulp. Therefore, any materials that are applied to dentine should not have any biologically detrimental effects or threaten the biological stability of the teeth.
Kanca demonstrated that if a primer having high hydrophilic property and an adhesive monomer having both hydrophilic and hydrophobic properties are used together, the bonding strength becomes stronger (see Japanese Laid Open Patent Publication Nos. 53-33687 and 54-10986, and Japanese Patent Application No. 56-120610). Thereafter, various compounds have been suggested, and the treating method has been further developed. Recently, products that exhibit excellent bonding strength were mainly used. These products were applied in a two-step procedure, first involving treatment with an acid etchant and a primer, an adhesive agent or an acid etchant, and then with a primer and an adhesive agent.
Also, in case of dentine adhesion, an acid etchant, a primer and an adhesive agent is applied in a one-step procedure. However, there is a problem in that the bonding strength obtained via the one-step procedure is lower than that obtained by the aforementioned two-step procedure.